This invention relates to a heat retaining appliance. More particularly, it relates to an appliance which is only initially electrically heated, retains its heat for a reasonable time, and slowly transmits this retained heat to food placed therein. This is desirable for heating the food, which "heating" shall mean herein elevating the temperature of a product and/or reducing the cool off rate of the product as much as possible. The latter eliminates the necessity for continued electrical heating of the food to maintain it at an elevated temperature.
Problems are encountered when food is served at a distance, either in time or space, from the place of its original preparation. This occurs when a meal is prepared in a central kitchen, but is served away from the kitchen sometime well after its preparation. To keep hot food hot, it has been known in the past to place the food in a container, such as a casserole, equipped with heating elements and an electrical cord for delivering electrical energy into the elements. However, the capability of moving such a container is restricted because it must be connected by the cord to a wall socket to keep the food hot. Thus, a "cordless" serving appliance is preferred.
Heat retaining appliances of this type are disclosed in U.S. Pat. Nos. 4,009,368; 3,937,209; 3,875,370; 3,720,198; 3,603,106; 3,463,140; 3,389,946; 3,148,676; and 2,640,478. Problems have arisen in connection with such appliances, particularly those that have a heat retaining material confined within a metal jacket, which may or may not be insulated and/or further encased by an outer plastic shell. It has been found that the rate of exchange or transfer of heat from the heat retaining material, through the metal jacket, and into the food heating area of such an appliance is too rapid. This is particularly a problem when the appliance is uncovered for serving the food because the heat being emitted from the heat retaining material is more apt to be lost to the environment.
Therefore, it is an object of the present invention to provide a heat retaining appliance which may initially be connected to an electrical energy source to be heated, but may then be disconnected therefrom, while still retaining heat for a reasonable time.
It is another object of the present invention to provide a heat retaining appliance having a mass of heat storing material enclosed within a casing shaped to receive a food-containing dish as well as a removable cover, the latter of which functions not only to protect food placed on the dish against contamination, but also to insulate the food and the appliance against loss of heat to the atmosphere, while maintaining the food hot for as long as possible.
It is another object of the present invention to provide a heat retaining appliance at least partially made of materials which exhibit heat transfer properties similar to that of plastic, so that effective heat transmission to the interior of the appliance is maximized while heat loss from the appliance is minimized.
It is still another object of the invention to provide a heat retaining appliance in which a substantially nonmetallic heat retaining material is confined within a substantially non-metallic housing and an insulating casing encloses the housing to retard heat loss from the appliance.